The present invention relates to a pressure transducer assembly for a process circuit used in a process plant.
In process plants, such as chemical and refining plants, pressure transducers installed on the site are used as field instruments to measure fluid pressure. Pressure transducers are used for example to measure the fluid pressure and to detect the extent that the process circuit is full of fluid. Measuring diaphragms with differential pressure transducers are frequently used to ascertain the fluid flow in the circuit.
A known pressure transducer assembly of this type (WO 97/22855) includes a fluid line between the process circuit and the pressure transducer. The fluid line is connected at both ends via flange connections to connections on the process circuit and on the pressure transducer.
In practice, the pressure transducer assembly is designed in this case as a differential pressure transducer assembly with two parallel fluid lines. The transducer and circuit connections to the process line consist of welded flange connection pieces. Similarly, flange connection pieces are welded on both fluid line ends and are then screwed to the flange connections on the process circuit and on the pressure transducer.
In a generally known pressure transducer assembly, the pressure transducer is located relatively far from the process circuit and is connected with long flexible fluid lines. Such a pressure transducer assembly is expensive, since the pressure transducer and the valve beneath it must be independently supported at a suitable location. The valve and the pressure transducer are then attached to each other. After the laborious installation of the valve and the pressure transducer, the very long fluid lines can be connected to the assembly. The long fluid lines are used in the prior art to prevent the overheating of the pressure transducer when hot fluids are to be carried. While the long fluid lines may reduce the overheating problem, they often produce inaccurate results, thereby defeating the purpose of the transducer assembly altogether.
In a pressure transducer assembly of this type (WO 97/22855) the assembly is constructed and held directly on the fluid line in order to reduce the installation costs, so that the fluid lines which are short and stable in this case may take over a support function for both the valve and the pressure transducer. When the fluid lines are used as a means of support in addition to both measuring and transporting fluids, the welds connecting the fluid lines to the arrangement are put under great stress. The strength of the entire assembly is thereby determined by the quality of these welded connections. This often works to the detriment of the assembly and the weld connections must be made precisely and expensively or else the entire arrangement will be rendered weak.
In addition, when short fluid lines are used in an effort to gain stability and accuracy while at the same time cutting costs, the flexibility and ability to rotate that the traditionally long fluid lines offered is lost. This means that the pattern of holes used in the flange connections must line up and fit exactly at both fluid line ends after the flanges have been welded on. If these hole patterns are off and twisted even minimally, a connection may no longer be possible because the tolerances cannot be compensated for.
Many types of flanges, including the oval and double-oval flanges or the circular disk flanges with varied hole patterns are used depending on where and for what applications they are to be used. Once the flange connection pieces have been welded to the ends of the fluid lines, the flange configuration becomes fixed and the possibility of interchanging the separate flange designs for increased flexibility is no longer a possibility.
A flange connection consisting of two parts with a separate flange that connects a manometer to a measuring bore is also known (German patent 939 292). The manometer is used to measure the differences in two fluid pressures. The changing temperatures of such an assembly, often causes radial movements of the manometer between the separate screwed on flange and the flange connection piece. In anticipation of this movement the separate flange is screwed on only tight enough to hold the manometer on. The resulting gaps allow the assembly to compensate for the expected operational radial shifts.
The above German patent also incorporates a flange pipe with a sliding guide which is placed over the flange connection pieces in an axial direction. The flange pipe then allows for compensation for the axial temperature influenced movements of the assembly as well. Because of a connection which allows for both radial and axial sliding, this design is not suitable to also serve a support function for an attached pressure transducer and valve.
Accordingly, an object of the invention is to develop a pressure transducer assembly that can be held together with a selection of interchangeable flange forms to achieve flexibility and the possibility of adaptation of the assembly to different demands.
It is also an object of the invention to eliminate the frequently experienced pressure transducer assembly problems with tolerances with respect to the alignment of the connection hold patterns.
The present invention maintains great mechanical strength of the assembly without relying on welding. By eliminating the permanent fixation which welding brings, the present invention allows for a flexibility previously unknown in an assembly which must be strong enough to serve a support function.